Field of the Invention
The present disclosure relates to a herbal composition for preventing or treating neurological diseases or improving brain or cognitive function. More particularly, it relates to a herbal composition for protecting nerve cells and improving neurological diseases, which includes an extract of Euphoria longan fruit, red sage and Gastrodia elata. 
Background of Technique
Dementia refers to severe loss of global cognitive ability without disorder of consciousness, leading to loss of mental (intellectual) ability and ability for social activities. Dementia may be caused by various causes and is accompanied by memory impairment, speech impediment, disturbance in visuospatial ability, apraxia, agnosia, impairment of computational ability, frontotemporal lobar degeneration, disturbance in executive function, or the like.
Dementia can be classified into Alzheimer's dementia, vascular dementia and other dementia according to occurrence. Alzheimer's disease is the leading cause of dementia, accounting for about 50-60%. It is known that the impairment of cognitive function and damage of nerve cells in patients with dementia are related with disorder in transport, generation, secretion and removal of neurotransmitters. Representative neurotransmitters are acetylcholine and glutamate. It is reported that patients with dementia show decrease and reduced function of the neurotransmitter acetylcholine in brain tissues, which is important in learning and memory. Glutamate is an important excitatory neurotransmitter playing a key role in learning and memory in the central nervous system. It is known that excess glutamate accumulated around nerve cells can cause oxidative stress by inhibiting the synthesis of the antioxidant glutathione in the nerve cells or induce death of the nerve cells by causing influx of calcium ions via the N-methyl-D-aspartate (NMDA) receptor. Since the causes of dementia are various, medications for dementia target various routes. Typical example is the acetylcholinesterase (AChE) inhibitor which inhibits the reduction of the neurotransmitter acetylcholine directly involved in the impairment of cognitive function. Tacrine (Cognex®), donepezil (Aricept®), rivastigmine (Exelon®) and galantamine (Reminyl®) are examples. However, tacrine has the adverse effect of hepatotoxicity (Leonard, World Psychiatry 3: 84-88 (2004)), donepezil has adverse effects including nausea, vomiting and diarrhea (Burns et al., Dement Geriatr Cogn Disord 10: 237-244 (1999)), rivastigmine has central and peripheral cholinergic adverse effects at high concentrations (Leonard, World Psychiatry 3: 84-88, 2004), and galantamine has adverse effect in the gastrointestinal tract (Tariot et al., Neurology 54: 2269-2276, 2000). Other medications include memantine (Ebixa®) that acts on the glutamate receptor (Reisberg et al., Am J Geriatr Psychiatry 10:1-122 (2002)) as well as anti-inflammatory and antioxidant drugs. However, since the causes of dementia are diverse and not fully elucidated, treatments with the medications are only temporary or limited. In addition, although many patents about compositions for improving memory are published and issued in Korea, there is no sure cure yet. Accordingly, there is a strong need for the development of a medication of dementia having an excellent effect of preventing and treating the impairment of cognitive function with less adverse effects.
Throughout the specification, a number of publications and patent documents are referred to and cited. The disclosure of the cited publications and patent documents is incorporated herein by reference in its entirety to more clearly describe the state of the related art and the present disclosure.